Light has got no direct effect on the rate of transpiration but indirectly it affects the rate in two ways firstly by controlling the stomatal opening and secondly by affecting the temperature. With the increase in the light intensity the rate of transpiration increases because the stomata get opened and the temperature increases. The rate of transpiration increases markedly in light and decreases in dark. There is a close relationship between the opening of stomata and presence of light.one of the raw materials for photosynthesis, its concentration affects the rate of photosynthesis markedly. Because of its very low concentration in atmosphere $(0.03$ per cent only) it acts as a limiting factor in natural photosynthesis.